Collaborative dialogue proposed by Swain (2000, 2005) is grounded on co-construction of knowledge by L2 learners drawing upon their shared resources. It is operationalized by Language Related Episodes (LREs). Different factors may have a bearing upon the quality of interaction during collaborative activities amongst them the proficiency of the interlocutors; since, the nature of collaborative activities calls for working in pairs or groups. Despite a wealth of evidence in theory and practice on the effectiveness of collaborative activities, the question that still remains a matter of debate is what type of proficiency pairing of L2 learners in collaborative work is more conducive to L2 development. This book contributes to the existing debate and explores the frequency and resolution of LREs produced by EFL learners during collaborative problem solving tasks on speech acts across different proficiency pairings.